A dielectric support bead or other dielectric support structure serves to support and to hold the center contact within the connector body of a coaxial connector. Important parameters relating to the performance of the connector are: the effective inner and outer diameter of the dielectric support structure, its effective dielectric constant, the impedance of the dielectric support structure and its axial length. The effective dielectric constant should be as low as possible for preventing electrical resonances of the dielectric support structure from occurring below the upper limit of the connector operating frequency range. In other words, a lower effective dielectric constant in the support structure helps to achieve a coaxial connector that can operate at a higher frequency limit.
U.S. Pat. No. 4,867,703, in which one of the present inventors is an inventor, discloses a dielectric support bead for holding the center conductor of a coaxial connector. The dielectric support bead includes three radially-extending legs, with each leg terminating in a shoe-like cylindrical support surface. There is an annular shroud extending radially integral with the three legs and with the three shoe-like support surfaces. This shroud serves as an environmental barrier or block for preventing contaminants, such as metal flakes, from migrating into internal portions of the connector. As can be seen from looking at the drawings in U.S. Pat. No. 4,867,703, the dielectric support bead shown therein has a complex configuration which is difficult and expensive to fabricate.
The purpose of the complex structure disclosed in the '703 patent is to reduce the total amount of dielectric material in the support head for reducing the effective dielectric constant of the support bead as a whole.
Another arrangement for reducing the total amount of dielectric material in a support bead is shown in FIG. 1 herein. The support bead 80 in FIG. 1 is the Hewlett Packard Bead. Three shallow holes 82 are drilled spaced 120.degree. apart on a first side of the bead. These shallow holes, which are drilled in an axial direction, do not penetrate all of the way through the bead 80, so that the undrilled remaining material serves as an environmental block. Then, three more shallow holes (not seen) spaced 120.degree. apart are drilled in an axial direction on the second side of the bead and do not penetrate all of the way through the bead. These latter three shallow holes are offset 60.degree. from the shallow holes 82 on the first side of the dielectric head, so that the holes on opposite sides of the bead alternate in occurrence with each other. It is difficult, time-consuming and expensive to drill six accurately positioned shallow holes (three on each axial end) in each support bead.
A third arrangement for reducing the total amount of dielectric material in a support bead is shown in FIG. 2. The support bead 84 in FIG. 2 is known as a "standard six-hole bead". Six holes 86 are drilled in an axial direction through the bead 84. It is difficult, time-consuming and expensive to drill six accurately positioned holes 86 extending axially through a support bead. Moreover, these six holes 86 only remove a modest percentage of the total material in the bead 84.
A fourth arrangement for reducing the total amount of dielectric material in a dielectric support structure for the center contact of a coaxial connector is called the Radiall star support design as is shown on page I51 from a catalog of RADIALL, INC., which we believe is a company in France having a manufacturing facility in Stratford, Conn. The catalog in which page I51 appears bears a copyright date of 1989.
Among the problems associated with the Radiall star support design are non-stability and non-rigidity with minimal mechanical strength. The four bowed Kapton strips retain their individual flexibilities and thereby cause flexibility in support for the inner contact with minimal mechanical strength in support of this inner contact.